There is an X-ray detector as one example of a radiation detector. The X-ray detector is provided with, for example, an array substrate including multiple photoelectric conversion parts (also referred to as pixels), and a scintillator provided on the multiple photoelectric conversion parts and converting an X-ray to fluorescence. The photoelectric conversion part is provided with a photoelectric conversion element converting the fluorescence from the scintillator to a signal charge, a thin film transistor switching storage and release of the signal charge, and a storage capacitor storing the signal charge or the like.
In general, the X-ray detector reads out the signal charge as follows. First, the detector recognizes X-ray incidence from a signal input externally. Next, the detector converts the stored signal charge into a voltage by an integration amplifier and reads out it by turning on a thin film transistor of the photoelectric conversion part performing reading after the passage of a pre-determined time (a time necessary for storing the signal charge).
However, in this way, since start of the operation of the X-ray detector depends on a signal from an external equipment, an external circuit synchronizing the signal from the external equipment (for example, a signal notifying X-ray irradiation from an X-ray source) is necessary. If the external circuit is provided, it is susceptible to noise or the like, in the case where circuit synchronization with the X-ray irradiation is impossible, it may be impossible to acquire an X-ray image.
Here, a thin film transistor as a semiconductor element is irradiated with the X-ray, a current flows due to a photoelectric effect between a drain electrode and a source electrode. The source electrode of the thin film transistor is electrically connected to a data line. Then, there has been proposed a technique detecting the incidence start time of the X-ray by detecting a difference between an integral value of a current flowing in the data line with irradiation of the x-ray and an integral value of a current flowing in the data line with no irradiation of the X-ray.
However, in this way, it results in that a difference between the detected current integral value and the current integral value detected once a time before is obtained. If the current integral value detected once a time before is slightly lower than a threshold value, the difference of the current integral values flowing in the data line is small, and the X-ray may be impossible to be detected. If there is a disturbance noise such as a low frequency noise when converting into the voltage, the voltage values of the respective integration amplifiers are off set. For that reason, the influence of the disturbance noise such as the low frequency noise becomes large, and it may be difficult to detect the incidence start time of the X-ray accurately.